Objectives We studied the effect of different proportion of chicken manure in total fertilizer input on the appearance and inner taste qualities, as well as the yields of Gala apples, to provide reference for the organic substitution in fruit production.

Methods In 2017, a localized fertilizer experiment was started in Lashan Comprehensive Experimental Base of the Research Institute of Pomology of Chinese Academy of Agricultural Sciences, Xingcheng City, Liaoning province. The tested apple cultivar was ‘Gala’/SH38/Shan Dingzi (Malus pumila Mill/SH38/Malus baccata (L.) Borkh.). Six treatments were set up: no fertilizer control (CK), 100% chemical fertilizer (100%CF), 75% chemical fertilizer + 25% chicken manure (25%CHM), 50% chemical fertilizer + 50% chicken manure (50%CHM), 25% chemical fertilizer + 75% chicken manure (75%CHM), and 100% chicken manure (100%CHM). At fruit ripening stage, 20 representative fruits were taken from each treatment plot, 10 fruits for measurement of the appearance quality, and 10 for taste.

Results Compared with 100%CF, 25%CHM and 50%CHM treatment did not impact the single fruit weight, while 75%CHM and 100%CHM treatment increased the single fruit weight significantly; 25%CHM, 50%CHM, and 75%CHM treatment did not affect fruit longitudinal and transverse diameter, while 100%CHM significantly increased the indexes. The manure substitution rates did not cause significant differences in the sunny side color, shade side lightness, red-green color difference, and yellow-green color difference of the fruits, but 50%CHM decreased the color saturation, and 75%CHM decreased the hug angle (P<0.05). Malic acid and quinic acid decide the tart and astringent flavor of fruit. The manure substitution rates did not influence fruit quinic acid content, but 75%CHM and 100%CHM fruits were recorded higher malic acid content than the 25%CHM and 50%CHM fruits. In addition, 100%CHM fruits had the highest titratable acid, the 75%CHM fruits had the highest esters (897.14 μg/g) and alcohols aroma substances (209.30 μg/g), the 25%CHM fruits had the highest aldehydes (48.20 μg/g) and ether aroma substances (6.76 μg/g), respectively. The results of the principal component analysis showed that the 75%CHM treatment had the highest overall score of 0.6291.

Conclusions Replacing chemical fertilizer with appropriate proportion of chicken manure can increase single fruit weight and size, form more saturated color of fruit, enhance malic acid, ester aroma substances, as well as total aroma substances that determine the flavor of the fruit. Without change the total nitrogen input, the appropriate ratio of chicken manure and chemical fertilizer N is 3∶1 for high quality and yield Gala apple production.